1. Field of the Invention
This invention relates to a method and an apparatus for controlling the direction of an excavating machine which uses a shield body provided with a head portion and a tail portion flexibly connected to the rear of the head portion, and more particularly, to a method and an apparatus for controlling the advancing direction of an excavating machine by use of a light beam directed along a reference line such as a planning line for a tunnel to be constructed.
2. Description of the Prior Art
In case of constructing a tunnel like a pipeline by means of a tunnel excavating machine of a shield type which uses a shield body provided with a head portion and a tail portion which are flexibly connected relatively to each other, the advancing direction of the excavating machine is corrected, that is, a so-called "directional control" is done, when the excavating machine is deviated from a planning line of a tunnel to be constructed by the excavating machine.
As one of these kinds of the methods and apparatuses for controlling the direction, a light beam such as a laser beam directed along the planning line of the tunnel to be constructed is used as a reference line for shift confirmation, and the advancing direction of the excavating machine, in particular, the direction of the head portion to the tail portion is corrected so that the light beam may be irradiated at the objective position in a target mounted on the tail portion to receive the light beam, in other words, so that the irradiating position of the beam to the target may become a predetermined place, that is, an objective position.
In this direction controlling method and apparatus known per se, the target is positioned so that a light beam may be irradiated at an objective position when both of the position and the attitude of the excavating machine relative to a planning line are in such a manner that the axis of the excavating machine corresponds to the planning line. For this reason, if the excavating machine is deviated from the planning line, the irradiating position of the beam to the target is deviated from the objective position. In this case, the advancing direction of the excavating machine is corrected so that the light beam may be irradiated at the objective position in the target in the direction controlling method and apparatus known per se.
In the direction controlling method and apparatus known per se using a light beam and a target, however, since the light beam directed along a reference line is directly irradiated to a target mounted on the tail portion, a directional correction is only made so that a target position where the target and the reference line intersect may be kept along the reference line. In such a directional control, there are many cases where the head portion is inclined against the tail portion or the reference line, even though a light beam may be irradiated at the objective position in the target, and therefore, the operation for the directional correction is complicated.
Also, in the direction controlling method and apparatus known per se as described above, the target position coincides with the reference line by shifting the top end of the head portion beyond the reference line. Therefore, the head portion is largely deviated from the reference line. Accordingly, in the direction controlling method and apparatus known per se as described above, the zigzag frequency of the head portion is not only high, but also the head portion is advanced in a zigzag way so as to largely deviate from the reference line. As a result, the excavating machine is advanced in a zigzag way so as to largely deviate from the reference line resulting in the complicated operation for the directional correction.
As one of other directional control apparatuses, either one of a dial plate and a pointer is mounted on the head portion and the other is mounted on the tail portion, respectively, the direction and the size of the bend of the head portion relative to the tail portion are confirmed on the basis of the position of the pointer on the dial plate and the advancing direction of the excavating machine, in particular, the direction of the head portion relative to the tail portion is corrected.
In the direction controlling method and apparatus known per se using the dial plate and the pointer, the direction and the size of the bend of the head portion relative to the tail portion can be confirmed. However, since it cannot be confirmed whether or not the excavating machine coincides with the reference line, the direction and the size of the bend of the head portion relative to the tail portion cannot be corrected so that the excavating machine coincides with the reference line, even if the direction and the size of the bend of the head portion relative to the tail portion may be corrected.
It can be considered that the directional control technique known per se by use of a light beam and a target and that known per se by use of a dial plate and a pointer are both used in order to correct the direction and the size of the bend of the head portion relative to the tail portion so that the excavating machine coincides with the reference line. However, since the direction and the size of the deviation of the irradiating position of the light beam to the target is independent of those of the deviation of the pointer relative to the dial plate, the directional correction has to be done by operators on the basis of mutually independent information, and the directional correction operation needs skills.